I have a 2008 34FK I purchased 6 months ago. Although the unit never "leaked" water where I could see it( I live in it full time and had several opportunities to check it during storms)it still had rotted damage to walls on both sides. The areas affected start at the top of the wall and measure about 48" long and go down from the top of the wall about 24"
According to my dealer, East Coast RV's in Roaring Spring PA, it is a common problem not usually noticed until the rot causes a soft wall.
The way to check for a problem is take a common hammer and tap the wall all along the inside close to ceiling. the soft spots will be obvious. Tap down to see how far down it goes
I have exposed my damaged area by cutting the inside paneling in the affected areas. The black stained plywood is rotted, and the hardware near the roof is rusted. I am carefully removing all of the plywood layers being extremely careful not to puncture the fibreglass on the outside. I am going to piece in a replacement section of plywood, glue it in place and bolt through the outside to clamp it with the special camtainer bolts used in FRP construction. And make damn sure the roof no longer leaks. I am going to leave the inside exposed until I am sure it is sealed.
The other option with this type of construction is simply to cut out the affected areas and piece in a new section. You would use the same aluminum 4 inch wide pieces they use at the bottom. The aluminum goes completely around the edge with the same sealants they use at the plant. Of course with this method a repair is obvious on the outside. The factory can sell you pieces to fit in, your dealer can help you get them
I called the plant and they said if the damage is bad enough they just replace entire sections of wall top to bottom. I have no idea how expensive that is.